Uncrewed Systems Technology 049 - April/May 2023

84 Dossier | Rotron Power RT600-HC redesign components for lower weight. For instance, the rotor housing is still cast from LM25 aluminium alloy, as it is a free-flowing casting material, and the end plates and centre plate are cast from LM13. After casting, these are heat- treated and subjected to non-destructive testing to confirm the absence of leaks. “We use precision sand casting, and we’veworked closely with foundries to removeweight, particularly in the end plates,” Head says. “We use either Hadleigh or Hayworth for the casting, and as well as being very capable they also use some sophisticated flow software to ensure the liquidmetal flows as expected.” After casting, the housing parts come to Rotron to be put through several processes in its machine shop, to make them ready for internal nickel silicon carbide electroplating by Poeton. After that, A&M EDM in Birmingham, England, performs precision grinding of the trochoid followed by wire-eroding, a form of electrical discharge machining (EDM). Head comments, “A&M don’t use abrasives; EDM is incredibly precise and reliable. It can cut hard metals with an accuracy of around 10 microns so long as you control the temperature well, and it leaves a good finish.” Some more post-processing in Rotron’s machine shop follows, before the housing parts are then checked on a coordinate measuring machine, before being given serial numbers and entered into the company’s parts stocks. Rotron can also supply modified versions of the end plates that come with integral mounting points for interfacing with gearboxes, belts and other ancillaries, although there is trade-off of a slight increase in weight for the easier ancillary systems installation. Shaft and rotor Some issues with the engine’s eccentric shaft, particularly when the engine was being used to drive large propellers through offset reduction drives, have been found and mitigated. “In short, we had some stress-raisers inside the end of it,” Head explains. “The shaft used to have a very deep bore on the inside, so we’ve reduced its length and fully radiused it to lessen any stress-raisers inside. It never had any issues when, say, driving a gearbox spindle, but we wanted a single shaft that would fit every application, so when we found this issue it was an obvious improvement to implement. It makes manufacturing a bit more challenging but ultimately it’s been worth it.” The rotor meanwhile has had some changes made to the orientation of its internal cooling fins for improved thermal management, along with some proprietary changes that Rotron declines to discuss. “We also brought all the gear cutting in-house, largely to control the tolerances ourselves – specific niche processes like backlashmeasurement and engine balancing,” Head explains. “We balance the rotors individually, then balance the April/May 2023 | Uncrewed Systems Technology Rotron has shifted towards bespoke engine designs and services for its UAV customers, for whom ancillary systems and ongoing support are as important as the core rotary engine technology